In Situ Thermal Annealing and Growth Investigations on III/V Semiconductor Materials
In order to handle toxic and phyrophoric precursors inside a TEM and therefore facilitate group V stabilized thermal annealing experiments, significant changes of the original in situ system (designed and produced by Protochips) are necessary. To further ensure safely when storing and transfering th...
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|Summary:||In order to handle toxic and phyrophoric precursors inside a TEM and therefore facilitate group V stabilized thermal annealing experiments, significant changes of the original in situ system (designed and produced by Protochips) are necessary. To further ensure safely when storing and transfering the precursors gases from the storage container to the manifold, a home made gas storage locker was built. Moreover, to prevent any type of contamination and ensure no precursor distributes into the air, the locker and the manifold form a closed system in which ultra pure N2 is used as a carrier and purge gas. If necessary it is possible to switch to pure Ar or a ArH2 (4%H2) mixture as carrier and purge gas. The home made gas storage locker provides three ports on the group III and group V side, respectively. These ports are mainly for the precursor container but can also be used to connect gas bottles if other purge and carrier gases are needed. All connections in the gas storage locker are welded where possible. If necessary, vacuum coupling radiation
(VCR) metal gasket face seals with silver-plated stainless steel seals are used. To ensure that no toxic gases are released into the environment, a mini absorber is installed in the exhaust pipe. To take fire safety into account the locker complies with DIN 12925. This means that it is fire safe and that all openings close automatically in case of a fire inside the locker. Furthermore, an external ventilation system ensures that no toxic gases are released into the air. To further ensure safety during the whole process of gas transfer to the manifold and during the experiment, the systems are monitored by gas sensors.
To be able to investigate cross-sectional samples of metal organic vapor phase (MOVPE) grown crystalline structures under atomic resolution condition inside the in situ cell holder which has just single tilt capabilities, it is necessary to deposit a electron transparent focussed ion beam (FIB) lamella precisely perpendicular to its zone axis on the thermal ￼￼e-chip. To realize this geometry a reproducible FIB preparation technique was developed, which results in a partial electron transparent lamella perfectly aligned perpendicular to the selected zone axis. Moreover, the electron transparent part of the lamella is well protected between the thicker areas which prevent bending of the area of interest during the thermal treatment. The first performance checks prove that it is possible to achieve atomic resolution due to the accurate FIB preparation presented in this work.
To check the functionality of the system and prove that it is possible to investigate groupV stabilized thermal annealing processes under high resolution condition, two annealing series of a Ga(N,As,P) sample were performed. During the first series N2 was present in the in situ holder, while the second series of measurements were carried out in a tertiarybutylphosphine (TBP) environment. The sample annealed in a TBP environment shows favorable thermal stability up to 500 ◦C compared to the unstabilized sample, which begins to degrade at less than 300◦C. Subsequent data analysis was able to track the P desorption from the material by measuring the thickness of the sample during thermal annealing with and without stabilization. This analysis enables the possibility to calculate and compare the activation energy (EA) of the P for the unstabilized and group V stabilized thermal annealing treatment.
Further investigation on the initial Bi cluster formation temperature and the cluster characteristic in terms of cluster size and formation time is determined by analysing the intensity distribution within Ga(P,Bi) layers with different fractions of Bi for three tem- perature series covering the MOVPE growth temperature regime. Due to the possibilities of the developed setup and the gained knowledge from the P desorption experiments on Ga(N,As,P), it was possible to study the dynamic Bi clustering processes in an environment which ensures that the results are not distorted by any destructive behavior of the crystal during the thermal treatment.
In addition to the group V stabilized thermal annealing experiment, GaP growth on Si was also investigated in the framework of this thesis. For these experiments facetted Si nanoparticles served as the Si substrate. By annealing the particle in an ArSiH4 (4 % SiH4) environment at 1000◦C for one hour, it was possible to remove the amorphous SiOx shell around the crystalline core. These first results prove that it is possible to grow GaP on Si inside the in situ cell; nevertheless, the growth parameters need further investigation to enable high quality growth of GaP on Si under high resolution conditions.|
|Physical Description:||101 Pages|